Pseudoxanthoma Elasticum (PXE) is an inherited connective tissue disease characterized by calcification of elastic fibers within the dermis, eye and vascular system. Cultured fibroblasts from patients with PXE and age and sex matched normal individuals have been studied in an effort to identify the biochemical lesion associated with this disease. Abnormal proteolytic activity that degraded sulfated proteoglycans was identified in tissue culture media from PXE fibroblasts. This protease activity has been partially purified and characterized. It has a maximum activity of pH 6 and is inhibited by mercury, iodoacetamide and peptidyl diazomethyl ketones; data that strongly suggests that the enzyme is a cysteine endopeptidase. Furthermore, the enzymatic activity is inhibited by EDTA and replacement of zinc to the enzyme preparation facilitates reactivation. The objective of the proposed work is to further purify this enzyme and complete its characterization. Then, we will study its role in the pathogenesis of PXE by evaluating its proteolytic action on elastic fibers. In addition, normal and PXE fibroblasts will be subcultured over elastin in tissue culture to determine whether we can establish an in vitro model for the calcification of the elastic fibers by PXE cells. Preliminary evidence from this laboratory about possible defects in lipid metabolism and the presence of gamma-carboxyglutamic acid in calcified elastic tissue has been obtained. We propose to pursue these lines of research in an effort to understand how these observations may fit into the pathogenesis of PXE.